Hybrid fin field-effect transistor structures and related methods

ABSTRACT

Abstract Semiconductor-on-insulator structures facilitate the fabrication of devices, including MOSFETs that are at least partially depleted during operation and FinFETs including bilayer fins and/or crystalline oxide.

RELATED APPLICATION

This application is a continuation application of U.S. Ser. No. 11/001,166, filed Dec. 1, 2004, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates generally to semiconductor structures and particularly to hybrid strained semiconductor-on-insulator structures.

BACKGROUND

As geometric transistor scaling becomes more difficult and less effective in providing adequate performance enhancements, there is an incentive to improve the performance of transistors by enhancing innate carrier mobility by, e.g., application of strain to the semiconductor channel material. Although process simplicity is maintained by the application of one type of strain (or one type of channel material) for both NMOS and PMOS devices, overall performance would be greatly improved if it were possible to enhance the performance of each type of device separately. Traditionally, this enhancement has been incomplete—one type of channel material is typically used for both device types, with selective application of strain to the channel material for each device.

Devices are advantageously formed on semiconductor-on-insulator (SOI) substrates. Such substrates offer the benefits of an insulating substrate, such as reduced parasitic capacitances and improved isolation.

SUMMARY

The efficacy of the traditional approach for enhancing the performance of NMOS and PMOS devices may be improved by additionally customizing the transistor channel materials and their respective strain levels selectively for NMOS and PMOS devices. This is particularly true for advanced transistor geometries such as partially depleted semiconductor-on-insulator (PDSOI) devices, fully depleted semiconductor-on-insulator (FDSOI) devices, or fin field-effect transistors (FinFETs).

Although schemes exist to utilize multilayer channel materials and/or types of strain for transistors (see, e.g., U.S. Ser. Nos. 10/456,926, 10/164,665, 10/177,571, and 10/216,085, and U.S. Pat. No. 6,730,551, all of which are incorporated herein by reference), these schemes may not be effective for FDSOI and PDSOI devices when the total desired channel thickness for each type of device is very small. Since some such schemes rely on the presence of two channels in the starting substrate, this bilayer scheme may not allow the device type that utilizes the top channel for conduction to operate in fully depleted mode (due to the total thickness of the two channels being too great for the device to meet the FD maximum thickness criterion).

In accordance with the invention, NMOS and PMOS devices have channel layers of different materials and/or types of strain, each with potentially a very thin thickness. Aspects of the invention include variations in the starting substrate/channel layer structure and/or the processes used during device fabrication to create the final structure. For these solutions, Si—Ge alloys are used as exemplary materials. In general, it has been demonstrated that layers of Si—Ge with low Ge contents and/or under tensile strain are preferred for NMOS devices, and layers with higher Ge content and/or under compressive strain are preferred for PMOS devices. Other combinations of materials, including group IV semiconductors such as alloys of Si, Ge, or SiGe with C; III-V semiconductors; and II-VI semiconductors may also be suitable.

In an aspect, the invention features a structure including (i) a semiconductor substrate, a first semiconductor layer including a first semiconductor material disposed over at least a first portion of the substrate, and a second semiconductor layer including a second semiconductor material disposed over at least a second portion of the substrate; (ii) a first MOSFET disposed on the substrate and including a first MOSFET channel disposed in a portion of the first semiconductor layer over a first insulating material, the first MOSFET channel including the first semiconductor material; and (iii) a second MOSFET disposed on the substrate and including a second MOSFET channel disposed in a portion of the second semiconductor layer over a second insulating material, the second MOSFET channel including the second semiconductor material.

The first and second MOSFETs are at least partially depleted during operation. Moreover, the first MOSFET and/or the second MOSFET may be fully depleted during operation. Each of the first and second MOSFETs may be an nMOSFET or a pMOSFET.

The first and/or semiconductor material may include or consist of a group IV material, a III-V material, and/or a II-VI material. Specific examples of such materials include silicon, SiGe, germanium, an array of carbon nanotubes, and mixtures or alloys thereof; and gallium arsenide, indium arsenide, indium gallium arsenide, indium phosphide, gallium nitride, indium antimonide, gallium antimonide, gallium phosphide, and mixtures or alloys thereof. At least one of the first and second semiconductor materials may be tensilely strained and/or compressively strained.

The first semiconductor layer may have a first crystalline orientation, the second semiconductor layer may have a second crystalline orientation, and the first crystalline orientation may be different from the second crystalline orientation. The first crystalline orientation may be selected from a {100} family of crystalline planes; the second crystalline orientation may be selected from a {110} family of crystalline planes.

The first semiconductor layer may have a first crystalline in-plane rotation, the second semiconductor layer may have a second crystalline in-plane rotation different from the first crystalline in-plane rotation.

A crystallographic orientation of the nMOSFET channel may be parallel to a crystallographic direction selected from any of a <110> family of crystallographic directions. A crystallographic orientation of the pMOSFET channel is parallel to a crystallographic direction selected any of a <100> family of crystallographic directions.

An insulator layer including the first and second insulating material may be disposed over the semiconductor substrate, with the first insulating material being identical or substantially similar to the second insulating material.

A first insulator layer including the first insulating material may be disposed over at least the first portion of the substrate, and a second insulator layer including the second insulator material may be disposed over at least the second portion of the substrate, such that the first MOSFET channel is disposed over the first insulator layer, and the second MOSFET channel is disposed over the second insulator layer.

The first semiconductor layer may be disposed over a region of the second semiconductor layer, with the first semiconductor layer having a first type of strain and a first lattice constant, and the second semiconductor layer having a second type of strain and the first lattice constant. Each of the first and second types of strain may be either of tensile or compressive strain.

The first semiconductor layer may have a first type of strain and a first lattice constant, and the second semiconductor layer may be disposed over a region of the first semiconductor layer, the second semiconductor layer having a second type of strain and the first lattice constant.

The first MOSFET may include a first gate dielectric layer (including a first dielectric material) disposed over the first MOSFET channel and the second MOSFET may include a second gate dielectric layer (including a second dielectric material) disposed over the second MOSFET channel. The first and second dielectric materials may be identical, substantially similar or substantially different. The first and/or the second dielectric material may include or consist of at least one of silicon dioxide, silicon oxynitride, silicon nitride, barium oxide, strontium oxide, calcium oxide, tantalum oxide, titanium oxide, zirconium oxide, hafnium oxide, aluminum oxide, lanthanum oxide, yttrium oxide, yttrium aluminate, lathanum aluminate, lanthanum silicate, yttrium silicate, hafnium silicate, zirconium silicate, and doped alloys, undoped alloys, mixtures, and/or multilayers thereof.

The first MOSFET may include a first gate electrode layer comprising a first conductive material disposed over the first MOSFET channel, and the second MOSFET may include a second gate electrode layer comprising a second conductive material disposed over the second MOSFET channel. The first and second conductive materials may be identical, substantially similar or substantially different.

The first and/or second conductive material may include at least one of doped polycrystalline silicon, doped polycrystalline SiGe, Al, Ag, Bi, Cd, Fe, Ga, Hf, In, Mn, Nb, Y, Zr, Ni, Pt, Be, Ir, Te, Re, Rh, W, Mo, Co, Fe, Pd, Au, Ti, Cr, Cu, and doped alloys, undoped alloys, mixtures, and/or multilayers thereof.

A portion of the first semiconductor layer may be disposed over the second portion of the substrate, and the second semiconductor layer may be disposed over the portion of the first semiconductor layer.

A portion of the second semiconductor layer may be disposed over the first portion of the substrate and the first semiconductor layer may be disposed over the portion of the second semiconductor layer.

The first insulator layer and/or second insulator layer may include a crystalline oxide layer, which may induces a strain in the first and second semiconductor layers. The crystalline oxide layer may include at least one of a multicomponent metal oxide and a dielectric material having a lattice constant of approximately 5.4 Å and a body-centered cubic structure.

The multicomponent metal oxide may include or consist of one or more metals selected from the group consisting of Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Cu. The multicomponent metal oxide may include or consist of at least one of barium strontium titanate, barium strontium zirconate, barium strontium hafnate, lead titanate, yttrium aluminate, lanthanum aluminate, lead zirconium titanate, hafnium silicate, zirconium silicate, strontium silicon oxide, zirconium silicon oxide, hafnium silicon oxide, hafnium oxide, zirconium oxide, strontium titanate, lanthanum oxide, yttrium oxide, titanium oxide, barium titanate, lanthanum aluminate, lanthanum scandium oxide, and/or aluminum oxide. The dielectric material may include or consist of at least one of cesium oxide, aluminum nitride, and lanthanum aluminum oxide.

The first insulator layer may include or consist of a first crystalline oxide that induces a first type of strain in the first semiconductor layer, and the second insulator layer may include a second crystalline oxide that induces a second type of strain in the second semiconductor layer.

The first insulator layer may induce a first strain in the first semiconductor layer, and the second insulator layer induces a second strain in the second semiconductor layer.

In another aspect, the invention features a method for forming a structure, the method including the steps of (i) providing a semiconductor substrate, (ii) defining a first portion of the substrate; (iii) defining a second portion of the substrate; (iv) providing a first insulating material over the first portion of the substrate; (v) providing a second insulating material over the second portion of the substrate; (vi) forming a first semiconductor layer including a first semiconductor material over at least the first portion of the substrate; (vii) forming a second semiconductor layer including a second semiconductor material over at least the second portion of the substrate; (viii) forming a first MOSFET on the substrate, the first MOSFET including a first MOSFET channel disposed in a portion of the first semiconductor layer over the first insulating material, the first MOSFET channel including the first semiconductor material; and (ix) forming a second MOSFET on the substrate, the second MOSFET including a second MOSFET channel disposed in a portion of the second semiconductor layer over the second insulating material, the second MOSFET channel including the second semiconductor material. The first and second MOSFETs are at least partially depleted during operation.

Defining the first and second portions of the substrate may include defining a shallow trench isolation region. The first insulating material may be identical to or substantially the same as the second insulating material and providing the first and second insulating materials may include forming an insulator layer over the substrate.

Forming the first semiconductor layer may include bonding the first semiconductor layer to the insulator layer. The first semiconductor layer may be formed over the first and second portions of the substrate and the second semiconductor layer may be formed over a second portion of the first semiconductor layer disposed over the second portion of the substrate. The second portion of the first semiconductor layer may be thinned prior to forming the second semiconductor layer. Forming the insulator layer, the first semiconductor layer, and/or the second semiconductor layer over the substrate may involve deposition.

Either of the first MOSFET or second MOSFET may be an nMOSFET or a pMOSFET.

The first semiconductor layer may be formed over the first and second portions of the substrate. The second semiconductor layer may be formed over the first semiconductor layer.

A portion of the second semiconductor layer disposed over the first semiconductor layer over the first portion of the substrate may be removed.

A regrowth layer may be formed over the first semiconductor layer disposed over the first portion of the substrate.

Forming the regrowth layer may include providing additional first semiconductor material and a total thickness of the first semiconductor layer and the regrowth layer may be approximately the same as a total thickness of the first semiconductor layer and the second semiconductor layer in a second portion of the substrate.

Providing the first and second insulating materials may involve deposition, and the first insulating material may be different from the second insulating material. Forming the first and second semiconductor layers may involve deposition, and the first semiconductor material may be substantially the same as or different from the second semiconductor material. At least one of the first and second insulating materials may include a crystalline oxide.

The first semiconductor layer may have a thickness selected from a range of 1-50 nm. The second semiconductor layer may have a thickness selected from a range of 1-50 nm. For particularly aggressive FDSOI devices, the first and/or second semiconductor layer may have a thickness more preferably selected from a range of 1-20 nm, or more preferably 1-10 nm.

In another aspect, the invention features a substrate having an insulator layer disposed thereon, and a FinFET disposed over the substrate. The FinFET includes (i) a source region and a drain region disposed in contact with the insulator layer; (ii) at least one fin extending between the source and the drain regions and comprising a bilayer; (iii) a gate disposed above the bilayer, extending over at least one fin and between the source and the drain regions; and a gate dielectric layer disposed between the gate and the fin.

The bilayer may include a second semiconductor material disposed over a first semiconductor material. The first semiconductor material and the second semiconductor material may be the same or different, and each may include or consist of a group IV material, a III-V material, and/or a II-VI material. The group IV material may be silicon, SiGe, germanium, an array of carbon nanotubes, and/or mixtures or alloys thereof. The III-V material may be gallium arsenide, indium arsenide, indium gallium arsenide, indium phosphide, gallium nitride, indium antimonide, gallium antimonide, gallium phosphide, and/or mixtures or alloys thereof.

At least one of the first and second semiconductor materials may be tensilely strained or compressively strained. The gate dielectric may be disposed proximate the first semiconductor material and the second semiconductor material.

In another aspect, the invention comprises a structure including a substrate having a crystalline oxide layer disposed thereon, and a FinFET disposed over the substrate. The FinFET includes (i) a source region and a drain region disposed in contact with the insulator layer; (ii) at least one fin extending between the source and the drain regions, the fin comprising a first semiconductor layer disposed over the crystalline oxide layer; (iii) a gate disposed above the first semiconductor layer, extending over at least one fin and between the source and the drain regions; and (iv) a gate dielectric layer disposed between the gate and the fin.

In another aspect, the invention comprises a structure including (i) a substrate; (ii) a first insulator layer disposed over at least a first portion of the substrate; (iii) a second insulator layer disposed over at least a second portion of the substrate; (iv) a first FinFET disposed over the substrate; and (v) a second FinFET disposed over the substrate. The first FinFET includes (i) a first source region and a first drain region disposed over and in contact with the first insulator layer; (ii) a first fin extending between the first source and the first drain regions, the first fin including a first semiconductor material disposed on at least one vertically oriented sidewall of the first fin; (iii) a first gate disposed above the substrate, extending over the first fin and between the first source and the first drain regions; and (iv) a first gate dielectric layer disposed between the first gate and the first fin. The second FinFET includes (i) a second source region and a second drain region disposed over and in contact with the second insulator layer; (ii) a second fin extending between the second source and the second drain regions, the second fin including a second semiconductor material disposed on at least one vertically oriented sidewall of the second fin; (iii) a second gate disposed above the substrate, extending over the second fin and between the second source and the second drain regions; and (iv) a second gate dielectric layer disposed between the second gate and the second fin. The first semiconductor material has a first crystalline orientation, the second semiconductor material has a second crystalline orientation that preferably differs from the first crystalline orientation.

The first insulator layer may include a first crystalline oxide, the second insulator layer may include a second crystalline oxide, the first fin may include the first crystalline oxide, and the second fin may include the second crystalline oxide.

The first crystalline oxide and the second crystalline oxide may be substantially different. The first fin and second fin may be substantially parallel. The first semiconductor material and the second semiconductor material may be substantially the same. The first crystalline orientation may be selected from a {100} family of crystalline planes or a {110} family of crystalline planes. The first FinFET may include an n-channel device and the second FinFET comprises a p-channel device.

In another aspect, the invention features a method for forming a structure, the method including (i) providing a substrate having an insulator layer disposed thereon, and a bilayer disposed in contact with the insulator layer, the bilayer including a second semiconductor layer disposed over a first semiconductor layer; and (ii) forming a FinFET on the substrate. The FinFET is formed by (i) patterning the bilayer to define a source region, a drain region, and at least one fin disposed between the source and the drain regions, (ii) forming a gate dielectric layer, at least a portion of the gate dielectric layer being disposed over the fin, and (iii) forming a gate over the gate dielectric layer portion disposed over the fin.

The bilayer may include or consist of at least one of a group II, a group III, a group IV, a group V, or a group VI element. The bilayer may include a strained semiconductor layer that may be tensilely strained or compressively strained.

In another aspect, the invention features a structure including (i) a substrate; (ii) a first FinFET disposed over the substrate; and (iii) a second FinFET disposed over the substrate. The first FinFET includes a first semiconductor material having a first crystalline orientation, the second FinFET includes a second semiconductor material having a second crystalline orientation, and the first and second crystalline orientations are different.

In another aspect, the invention features a method for forming a structure, the method including providing a substrate having an insulator layer disposed thereon, and a first semiconductor layer disposed in contact with the insulator layer; and forming a FinFET on the substrate. The FinFET may be formed by (i) patterning the first semiconductor layer to define a source region, a drain region, and at least one fin disposed between the source and the drain regions, (ii) selectively depositing a second semiconductor layer over a top surface of at least one fin to form a bilayer, (iii) forming a gate dielectric layer, at least a portion of the gate dielectric layer being disposed over the fin, and (iv) forming a gate over the gate dielectric layer portion disposed over the fin.

In another aspect, the invention features a method for forming a structure, the method including providing a substrate having a crystalline oxide layer disposed thereon, and a first semiconductor layer disposed in contact with the crystalline oxide layer; and forming a FinFET on the substrate. The FinFET is formed by (i) patterning the first semiconductor layer to define a source region, a drain region, and at least one fin disposed between the source and the drain regions, (ii) forming a gate dielectric layer, at least a portion of the gate dielectric layer being disposed over the fin, and (iii) forming a gate over the gate dielectric layer portion disposed over the fin.

In another aspect, the invention features a method for forming a structure, the method including (i) providing a substrate having a first semiconductor layer disposed thereon; (ii) defining a fin in the first semiconductor layer, the fin having an aspect ratio; and (iii) removing top portion of the fin, and thereafter selectively depositing a second semiconductor layer over the top portion of the fin so as to preserve the aspect ratio of the fin.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-15 are a series of schematic cross-sectional views of several alternative semiconductor structure illustrating processes for fabricating the structures; and

FIGS. 16-33C are schematic cross-sectional and top views of substrates illustrating a method for fabricating a FinFET.

Like-referenced features represent common features in corresponding drawings.

DETAILED DESCRIPTION

Referring to FIG. 1, a semiconductor-on-insulator substrate (SOI) 100 includes a semiconductor substrate 110 that itself includes or consists of a semiconductor material, such as silicon, germanium, SiGe, silicon carbide, gallium arsenide, indium phosphide, and/or gallium nitride. An insulator layer 120, e.g., a continuous buried insulating layer, is disposed over the semiconductor substrate 110. Insulator layer 120 may include or consist of, for example, silicon dioxide (SiO₂), silicon nitride (Si₃N₄ or other compositions), aluminum oxide, magnesium oxide, and/or other dielectric materials, or may be a multilayer structure including one or more different materials. The insulator layer 120 may have a thickness t₀ of, e.g., 50-200 nanometers (nm). For highly scaled devices, e.g., devices with gate lengths shorter than 100 nm, the insulator layer 120 may be relatively thin, i.e., have a thickness to of, e.g., 10-50 nm for better control of short channel effects. In an embodiment, SOI substrate 100 may include a single insulating substrate (not shown), rather than the combination of semiconductor substrate 110 and insulator layer 120. The single insulating substrate may be formed from an insulating material such as SiO₂, silicon nitride, glass, aluminum oxide, an organic polymer, plastic, or some combination of materials.

The SOI substrate may be a commercially available substrate that may be obtained from, e.g., SOITEC Silicon on Insulator Technologies of Bernin, France.

A first semiconductor layer 130 is disposed over the insulator layer 120. The first semiconductor layer 130 may include or consist of a first semiconductor material suitable for use as a channel of a MOSFET, such as at least one of a group IV material, e.g., silicon, SiGe, germanium, or an array of carbon nanotubes; a III-V material such as gallium arsenide, indium arsenide, indium gallium arsenide, indium phosphide, gallium nitride, indium antimonide, gallium antimonide, gallium phosphide; or a II-VI material, and mixtures or alloys including one or more of the aforementioned materials. The first semiconductor layer 130 may be strained, including tensilely or compressively strained, e.g., tensilely or compressively strained silicon. In some embodiments, the first semiconductor layer 130 may include approximately 100% Ge, and may be compressively strained. The first semiconductor layer 130 may have an initial thickness t₁ of, e.g., 1-50 nm, more preferably 1-20 nm for fully depleted devices, most preferably 1-10 nm or even 1-5 nm.

The first semiconductor layer 130 may initially be formed on a handle wafer (not shown) and then bonded to the insulator layer 120. For example, a handle wafer may include a Si_(1-x)Ge_(x) layer with x>0. A silicon layer formed over this Si_(1-x)Ge_(x) layer will be tensilely strained, and remains tensilely strained after being bonded to the insulator layer 120 to form the first semiconductor layer 130. A germanium layer formed over this Si_(1-x)Ge_(x) layer will be compressively strained, and remains compressively strained after being bonded to the insulator layer 120 to form the first semiconductor layer 130. Alternatively, strain in the first semiconductor layer may arise from mechanical deformation of the handle wafer or from thermal mismatch with the handle wafer. For example, the handle wafer may be mechanically biaxially or uniaxially strained by bending or heated to elevated temperature prior to bonding to insulator layer 120. After the handle wafer is removed, first semiconductor layer 130 will remain strained. See, for example, U.S. Ser. No. 10/456,103, filed Jun. 6, 2003, incorporated herein in its entirety.

A conductive layer (not pictured) may be disposed beneath insulator layer 120. This conductive layer may be used in subsequently formed devices as a ground plane or as a second gate in, e.g., in a planar double-gate transistor. This conductive layer may include the same material as may be used for a gate electrode, e.g., doped polycrystalline silicon, doped polycrystalline SiGe, Al, Ag, Bi, Cd, Fe, Ga, Hf, In, Mn, Nb, Y, Zr, Ni, Pt, Be, Ir, Te, Re, Rh, W, Mo, Co, Fe, Pd, Au, Ti, Cr, Cu, and doped or undoped alloys, or mixtures or multilayers thereof.

During device fabrication, a first portion 140 of the substrate 100 and a second portion 150 of the substrate 100 may be defined as shown in FIG. 2. The first and second substrate portions 140, 150 may be defined by, e.g., the formation of a shallow trench isolation (STI) region 160. The STI region 160 may be formed by methods known in the art, e.g., as described in co-pending U.S. Ser. No. 10/794,010, publication No. 2004/0173812 A1, incorporated by reference herein in its entirety.

A first MOSFET may be fabricated on the first portion 140 of the substrate 100 and a second MOSFET may be fabricated on the second portion 150 of the substrate 100 as follows. After STI 160 has been defined, a first portion 170 of the first semiconductor layer 130 disposed over the first portion of the substrate 100 may covered by a mask 180. The mask 180 may be formed from a masking material selected to be stable during the formation of a second layer comprising a second material over the second portion of the substrate. Moreover, the masking material is selected such that it may be selectively removed with respect to the second semiconductor layer, as described below. The masking material may include or consist of a dielectric material, such as silicon dioxide, silicon oxynitride, or silicon nitride.

In an embodiment, the first MOSFET is an nMOSFET and the second MOSFET may be a pMOSFET. In another embodiment, the first MOSFET is a pMOSFET and the second MOSFET may be an nMOSFET. In yet another embodiment, both the first and second MOSFETs are both nMOSFETs or pMOSFETs.

Mask 180 may be defined after the completion of STI formation. Alternatively, mask 180 may include masking material used to protect those regions of the first semiconductor layer that are not removed during STI formation; after STI formation, the masking material may be selectively removed from the second portion of the substrate where the pMOSFET will be formed, thereby exposing the portion of the first semiconductor layer disposed over the second portion of the substrate. Masking material used during STI formation may be, for example, a silicon nitride chemical-mechanical polishing (CMP) stop layer 182 disposed over a pad oxide layer 184.

Referring to FIG. 2 as well as to FIG. 3, a second semiconductor layer 200 may be formed over an exposed surface of a second portion 210 of the first semiconductor layer 130 that is disposed over the second portion 150 of the substrate 100. The second semiconductor layer 200 may include or consist of a material suitable for use as a channel of a MOSFET, e.g., a group IV material such as silicon, SiGe, germanium, or an array of carbon nanotubes; a III-V material such as gallium arsenide, indium arsenide, indium gallium arsenide, indium phosphide, gallium nitride, indium antimonide, gallium antimonide, or gallium phosphide; and a II-VI material, or mixtures or alloys including one or more of the aforementioned materials. The second semiconductor layer 200 may be strained, including tensilely or compressively strained, e.g., tensilely or compressively strained silicon.

The second semiconductor layer 200 may be formed by a deposition process, such as chemical-vapor deposition (CVD) or atomic layer deposition (ALD). CVD includes the introduction of multiple reagents into a reactor simultaneously. ALD includes the sequential introduction of multiple reagents into a reactor, including, but not limited to, atomic layer epitaxy, digital chemical vapor deposition, pulsed chemical vapor deposition, and other like methods.

A thickness t₂ of the second semiconductor layer 200 may be selected to be thick enough to enable carrier conduction, e.g., in the channel of a subsequently formed transistor, while preferably thin enough to support fully depleted device operation. The second semiconductor layer 200 may have a thickness t₂ of, e.g., 1-50 nm, more preferably 1-20 nm, most preferably 1-10 nm or even 1-5 nm for fully depleted devices.

In some embodiments, a total thickness t₃ of the first semiconductor layer 130 initial thickness t₁ and the second semiconductor layer thickness t₂ may be too great to allow fully depleted operation of devices formed on the second semiconductor layer 200. It may be advantageous, therefore, to reduce the initial thickness t₁ of at least that portion of the first semiconductor layer 130 disposed over the second portion 150 of the substrate, prior to the formation of the second semiconductor layer 200. The initial thickness t₁ of the first semiconductor layer 130 may be selectively reduced over the second portion 150 of the substrate by etching, e.g., by reactive ion etching (RIE) or by an in-situ etch prior to deposition in the deposition tool. For example, in an embodiment in which the first semiconductor layer 130 is silicon, the exposed portion 210 of the first semiconductor layer may be thinned in a chlorine-containing ambient including, e.g., hydrogen chloride or chlorine, to a reduced thickness t₄ of, e.g., 1-10 nm. The reduced thickness t₄ is thin enough such that the total thickness t₃ of reduced thickness t₄ and second semiconductor layer thickness t₂ will enable fully depleted device operation. The reduced thickness t₄ may be thick enough such that the remaining portion of the first semiconductor layer 130 does not agglomerate during subsequent thermal processing prior to and including the deposition of second semiconductor layer 200. Subsequently, the second semiconductor layer 200 may be deposited over the exposed portion 210 of the first semiconductor layer 130, such that the total thickness t₃ of the second semiconductor layer 200 and the thinned first semiconductor layer 130 is less than 50 nm, i.e., a sufficiently small thickness for the formation of fully depleted devices. In some embodiments, the total thickness t₃ of the reduced first semiconductor layer 130 thickness t₄ and the second semiconductor layer 200 thickness t₂ may be approximately the same as t₁, i.e., the initial thickness of the first semiconductor layer 130.

In practice, the total thickness t₃ of the first semiconductor layer 130 and the second semiconductor layer 200 is preferably 0.25 to 0.7 times a gate length of a transistor to be formed over the first and second semiconductor layers 130, 200. If the portion of the first semiconductor layer 130 disposed over the second portion of the substrate is completely removed, the thickness t₂ of the second semiconductor layer 200 may be 0.25 to 0.7 times a gate length of a transistor formed solely over the second semiconductor layer 200. Similarly, in a transistor formed solely over the first semiconductor layer 130, the initial thickness t₁ of the first semiconductor layer preferably may be 0.25 to 0.7 times a gate length of that transistor. Selection of a semiconductor layer thickness in the range of 0.25 to 0.7 times a transistor gate length may be preferable for improved operation of the transistor, as this relationship between the semiconductor layer thickness and the transistor gate length may enable fully depleted behavior in the transistor.

In an embodiment, the first semiconductor layer 130 includes relaxed silicon. A compressively strained second semiconductor layer 200 may be formed by thinning the first semiconductor layer 130 and depositing the second semiconductor layer 200 such that the second semiconductor layer 200 includes compressively strained SiGe.

In another embodiment, the first semiconductor layer 130 includes strained silicon. To obtain a compressively strained second semiconductor layer 200, the first semiconductor layer 130 may be thinned and the second semiconductor layer 200 deposited, the second semiconductor layer 200 including compressively strained Si_(1-x)Ge_(x) material having a Ge content x greater than that of the Si_(1-x)Ge_(x) of a handle wafer over which the first semiconductor layer 130 has been formed.

More generally, a compressively strained second semiconductor layer 200 may be formed from a material having a relaxed lattice constant greater than the strained lattice constant to which the first semiconductor layer 130 is strained, i.e., the second semiconductor material may have a relaxed lattice constant greater than that of the handle wafer on which the first semiconductor layer has been formed (and which induced strain in the first semiconductor layer). The deposition of such a second semiconductor material on the tensilely strained first semiconductor layer will cause the second semiconductor layer 200 to be compressively strained to the same lattice constant to which the first semiconductor layer 130 is strained.

As an example, consider the lattice constants of three different materials. The lattice constant of relaxed silicon is less than the lattice constant of relaxed Si_(0.5)Ge_(0.5), which is less than the lattice constant of relaxed germanium. Strained silicon grown on relaxed Si_(0.5)Ge_(0.5) will have a lattice constant of the relaxed Si_(0.5)Ge_(0.5) and will be tensilely strained. Strained germanium grown on relaxed Si_(0.5)Ge_(0.5) will also have the lattice constant of the relaxed Si_(0.5)Ge_(0.5), but will be compressively strained. Therefore, if the first semiconductor layer is substantially 100% strained silicon with the lattice constant of relaxed Si_(0.5)Ge_(0.5), the second semiconductor layer, in order to be compressively strained, has a lattice constant greater than that of relaxed Si_(0.5)Ge_(0.5).

In an alternative embodiment, the first semiconductor layer 130 may be a compressively strained germanium layer suitable for the formation of a pMOSFET. Then, the first semiconductor layer 130 may be thinned over a first portion 140 of the substrate 100 over which an nMOSFET will be formed. The second semiconductor material may include a material suitable for use as the channel of an nMOSFET, such as a group IV material, e.g., silicon, SiGe, germanium, or an array of carbon nanotubes; a III-V material such as gallium arsenide, indium arsenide, indium gallium arsenide, indium phosphide, gallium nitride, indium antimonide, gallium antimonide, or gallium phosphide; or a II-VI material, and mixtures or alloys including one or more of the aforementioned materials.

Referring to FIG. 4, a gate dielectric layer 220 may be formed over the first and second semiconductor layers 130, 200 by, e.g., deposition or growth. The gate dielectric layer 220 may be formed by one or more of a number of techniques, such as molecular beam epitaxy (MBE), oxidation, nitridation, CVD, ALD, or a combination of these or other methods. The gate dielectric layer may include or consist of a dielectric material such as, for example, silicon dioxide (SiO₂), silicon oxynitride (SiO_(x)N_(y)), silicon nitride (Si₃N₄ or other compositions), barium oxide (BaO), strontium oxide (SrO), calcium oxide (CaO), tantalum oxide (Ta₂O₅), titanium oxide (TiO₂), zirconium oxide (ZrO₂), hafnium oxide (HfO₂), aluminum oxide (Al₂O₃), lanthanum oxide (La₂O₃), yttrium oxide (Y₂ 0 ₃), yttrium aluminate, lathanum aluminate, lanthanum silicate, yttrium silicate, hafnium silicate, zirconium silicate, and doped or undoped alloys, mixtures or multilayers, thereof.

Alternatively, the first and second gate dielectric layers may include first and second dielectric materials that are identical or substantially similar. Essentially, a single gate dielectric layer 220 may be utilized over the first and second substrate regions 140, 150.

A gate electrode layer 230 may be formed over the gate dielectric layer by, e.g., CVD or ALD, and subsequently patterned to define a gate. The gate electrode layer 230 may include or consist of a suitably conductive material such as, for example, doped polysilicon, doped polycrystalline SiGe, Al, Ag, Bi, Cd, Fe, Ga, Hf, In, Mn, Nb, Y, Zr, Ni, Pt, Be, Ir, Te, Re, Rh, W, Mo, Co, Fe, Pd, Au, Ti, Cr, Cu, and doped or undoped alloys, mixtures or multilayers thereof. Gate electrode layers of different materials and/or compositions may be utilized over the first and second substrate regions 140, 150, i.e., a first electrode layer including a first conductive material may be formed over the first substrate region 140, a second electrode layer including a second conductive material may be formed over the second substrate region 150, and the first and second conductive materials may be substantially different.

Alternatively, the first gate electrode layer may include a first conductive material, the second gate dielectric layer may include a second conductive material, and the first and second conductive materials may be identical or substantially similar. Essentially, a single gate electrode layer 230 may be utilized over both first and second substrate regions.

The use of two different channel materials may facilitate the use of a single midgap metal gate for nMOSFET and pMOSFET devices, e.g., a gate electrode having a workfunction between that of n⁺ polysilicon (approximately 4.2 eV) and p⁺ polysilicon (approximately 5.2 eV) and preferably approximately 4.4-4.9 eV, such as titanium nitride (TiN), tantalum nitride (TaN), tantalum silicon nitride (TaSiN), tungsten (W), molybdenum (Mo), titanium (Ti), tantalum (Ta), polycrystalline carbon (C), or silicides of nickel or other metals (e.g., NiSi), thus making device fabrication less complex in comparison to the use of two different gate electrodes.

Portions of the gate electrode layer 230 and gate dielectric layer 220 may be removed as shown in FIGS. 4 and 5 by, e.g., etching to define first and second gate electrodes 240 a, 240 b disposed over the first and second semiconductor layers 130, 200, respectively. Sidewall spacers 250 may be defined proximate the gate electrodes 240 a, 240 b. Source and drain regions 260 may be formed for nMOSFET and pMOSFET devices by, e.g., implanting or diffusing appropriate dopants proximate the gate electrodes 240 a, 240 b, as is known in the art.

The source and drain regions 260 may also include a semiconductor material (which may be different from the semiconductor material disposed in nMOSFET channel 270 a and pMOSFET channel 270 b) defined in the first and second semiconductor layers 130, 200, respectively, beneath the gate electrodes 240 a, 240 b. Such a source/drain material may be formed by deposition(e.g., CVD or ALD), which may be preceded by an etch that removes at least some of the preexisting material present in the source and drain regions 260. The source/drain material may induce strain in the device channels 270 a, 270 b because of a difference in lattice constant and/or coefficient of thermal expansion between the source/drain material and the channel materials disposed beneath the gate electrodes 240 a, 240 b. The source/drain material may also serve to decrease series or contact resistance in the nMOSFET and pMOSFET devices. The source/drain material may also enable silicidation of the source and drain regions, as the initial thickness t₁ of first semiconductor layer 130 and/or thickness t₃ (the reduced thickness t₄ of the first semiconductor layer 130 in addition to thickness t₂ of second semiconductor layer 200) present in the source and drain regions may not be sufficient to enable formation of a low-resistivity silicide.

A self-aligned silicide (salicide) may be formed in source and drain regions 260 and optionally on top of first and second gate electrodes 240 a, 240 b as follows. A conductive layer is formed over the substrate 100. For example, a metal such as titanium, platinum, zirconium, cobalt, nickel, or alloys, mixtures, or multilayers thereof is deposited by, e.g., CVD or sputtering, with the conductive layer having a thickness of, e.g., 50-200 Å. In some embodiments, additional semiconductor material is formed over source and drains 260 regions, and optionally over the gate electrodes 240 a, 240 b, prior to the formation of the conductive layer, to define raised source and drain regions. An anneal is performed to react the conductive layer with source and drain regions 260 and optionally with tops of first and second gate electrodes 240 a, 240 b. Anneal parameters may be, for example, 400-800° C. for 1-120 seconds. Unreacted portions of the conductive layer disposed directly over insulator material, such as sidewall spacers 250, are removed by a chemical strip. A suitable chemical strip is a solution including H₂SO₄:H₂O₂ at a ratio of 3:1. A second anneal may be performed to further lower resistivity of the salicide. The second anneal parameters may be, for example, 600-900° C. for 1-120 seconds.

An nMOSFET 280 includes channel 270 a disposed in a portion of the first semiconductor layer 130 over a first insulating material 120 a, such that the nMOSFET channel 270 a includes the first semiconductor material. A pMOSFET 290 includes channel 270 b disposed in a portion of the second semiconductor layer 200 over a second insulating material 120 b, such that the pMOSFET channel 270 b includes the second semiconductor material. In some embodiments, insulator layer 120 including the first and second insulating materials is disposed across the semiconductor substrate 110, and the first and second insulating materials may be identical or substantially similar. In other embodiments, a first insulator layer including the first insulating material is disposed over a first portion of the semiconductor substrate 110, a second insulator layer including the second insulating material is disposed over a second portion of the semiconductor substrate 110, and the first and second insulating materials are substantially different. This embodiment is described in greater detail with respect to FIGS. 12-15.

The channels of the nMOSFET and pMOSFET may include one or more channel dopants, e.g., boron, arsenic, antimony, phosphorous, or indium. Such channel dopants may be of a type opposite the dopant type present in the source and drain regions of a particular device, and may influence control of the device threshold voltage. For example, the nMOSFET may include arsenic doping in the source and drain regions and boron in the channel region. These dopants may be present at a fairly low level, e.g., at a level less than 10¹⁶-10¹⁷ cm⁻³. In an embodiment, these channel dopants may be present at a level less than 10¹⁵ cm⁻³.

In some embodiments, the nMOSFET and the pMOSFET devices 280, 290 have different gate dielectric compositions and/or different gate electrode compositions. This may be achieved by the utilization of gate dielectric layers of different materials and/or compositions over the first and second substrate regions 140, 150, i.e., a first dielectric layer 220 a including a first dielectric material may be disposed over the first substrate region 140, a second dielectric layer 220 b including a second dielectric material may be disposed over the second substrate region 150, and the first and second dielectric materials may be substantially different. Two different types of dielectric layers 220 a, 220 b and gate electrode layers may be formed by the use of a “dummy gate” process. Here, the nMOSFET and pMOSFET devices 280, 290 are formed as described above, with the use of single gate dielectric layer 220. After the formation of sidewall spacers 250, a thick oxide layer may be formed over the nMOSFET and pMOSFET devices 280, 290 and planarized by, e.g., CMP, to expose top portions of the first and second gate electrodes 240 a, 240 b. A mask may be formed over, e.g., the nMOSFET device 280 to protect the gate electrode 240 a. The gate electrode 240 b and the underlying gate dielectric material of the pMOSFET 290 may be removed by, e.g., a wet etch. A second gate dielectric layer 220 b including a second dielectric material and a second gate electrode 240 b may be defined for the pMOSFET 290. The second dielectric material may be substantially different from the first dielectric material. The second gate electrode material may be substantially different from the first gate electrode material. A second planarization step may be performed to remove residual materials such as masks, as well as portions of the second gate dielectric material and second gate electrode material that are not needed for the second gate dielectric layer and the second gate electrode. Finally, the thick oxide is removed by, e.g., a wet etch.

As used herein, a “fully depleted” SOI device is fully depleted between the channel and the underlying insulating layer when the gate voltage is equal to the device's threshold voltage. The region between the channel and the underlying insulating layer is considered to be fully depleted if it is substantially free of charge carriers. The nMOSFET may be fully depleted during operation, and the pMOSFET may be fully depleted during operation.

During device operation, both the nMOSFET and the pMOSFET may have similar body thicknesses, i.e., similar total thicknesses of layers disposed beneath the gate, and both device types may have carrier depletion regions beneath the respective channels that extend to the underlying insulator layer.

Partially depleted on-insulator devices may be formed over particular regions of the substrate by modification of the above technique. More specifically, the body thickness, i.e., the thickness of the first or second semiconductor layers, may be sufficiently increased for certain devices to allow partially depleted operation. As used herein, a “partially depleted” SOI device is not fully depleted between the channel and the underlying insulating layer when the gate voltage is equal to the device's threshold voltage. When a region is not fully depleted, it is not substantially free of charge carriers.

An alternative starting material may be used to form the semiconductor structure having a first material disposed over a first portion of the substrate and a second material disposed over a second portion of the substrate, as illustrated in FIG. 3. A bilayer semiconductor layer structure 300 may be formed over the insulator layer 120 disposed on substrate 110 as shown in FIG. 6. This bilayer 300 includes first semiconductor layer 130 and second semiconductor layer 200 disposed over the first semiconductor layer 130. The second semiconductor layer 200 may include any material particularly suitable for either nMOSFET or pMOSFET operation. For example, for use in a pMOSFET device, the bilayer structure may be thin, having a total thickness t₅ of, e.g., 1-50 nm. The second semiconductor layer 200 may be any material suitable for use as a channel of a pMOSFET and may include, e.g., unstrained or strained germanium. The second semiconductor layer 200 may constitute the majority of the thickness of the bilayer 300. The underlying first semiconductor layer 130 may include any material suitable for use as a channel of an nMOSFET, e.g., unstrained or strained silicon.

The presence of a thin first semiconductor layer under the second semiconductor layer in a pMOSFET will not disturb operation of the pMOSFET, and may serve as a template for epitaxial formation of a thicker regrowth layer including the first semiconductor material, as described below, for use as a channel of an nMOSFET.

First and second portions 140, 150 of the substrate 100 may be defined as shown in FIG. 7 by, e.g., the formation of STI region 160, as described above with reference to FIG. 2.

After STI 160 has been defined, a first portion 310 of the second semiconductor layer 200 may be exposed while a second portion 320 of the second semiconductor layer 200 (disposed over the second portion 150 of the substrate 100) is covered by mask 180. The mask 180 may be formed from a masking material selected such that the material is stable during the removal of the first portion 310 of the second semiconductor layer 200 and the formation of a regrowth layer comprising a first material over the first portion 140 of the substrate 100. Moreover, the masking material is desirably selected such that it may be selectively removed with respect to the first semiconductor layer 130, as described below. The masking material may include a dielectric material, such as silicon dioxide, silicon oxynitride, or silicon nitride.

Mask 180 may be defined after the completion of STI 160 formation. Alternatively, mask 180 may include masking material used to protect those regions of the bilayer that are not removed during STI formation; after STI formation, the masking material may be selectively removed from the first portion of the substrate where the nMOSFET will be formed, thereby exposing the portion of the second semiconductor layer disposed over the first portion of the substrate. Masking material used during STI formation may be, for example, a silicon nitride CMP stop layer 182 disposed over pad oxide layer 184.

The exposed portion 310 of the second semiconductor layer 200 disposed over the first portion 140 of the substrate 100 may be removed as shown in FIGS. 7 and 8 by, e.g., RIE or by an in-situ etch prior to regrowth in the deposition tool. After the removal of the exposed second semiconductor layer portion 310, a first portion of the first layer 130 will be exposed. A regrowth layer 330 including the first material may be formed over the exposed first portion of the first layer 130, thus providing a single layer including the first material for subsequent use as a channel for an nMOSFET device.

After the regrowth of the first semiconductor layer, one obtains the same structure illustrated in FIG. 3. An nMOSFET may be formed over the first portion 140 of the substrate 100 and a pMOSFET may be formed over the second portion 150 of the substrate 100, as described above with reference to FIGS. 4 and 5.

In both embodiments, a final structure may include nMOSFET and pMOSFET devices, with each type of device having a channel of approximately the same thickness, one type having a single-layer channel and the other having a bilayer channel.

In an embodiment, regrowth layer 330 includes a semiconductor material included in first and second semiconductor layers 130, 200. In this case, deposition of regrowth layer 330 may result in first and second portions 140, 150 of substrate 100 both including bilayers being different combinations of materials. Referring to FIGS. 7 and 8B, in another embodiment, exposed second semiconductor layer portion 310 is not completely removed prior to deposition of regrowth layer 330. In this case, deposition of regrowth layer 330 in first portion 140 of substrate 100 may result in a trilayer structure 335 including a portion of first semiconductor layer 130, a portion of second semiconductor layer 200, and regrowth layer 330. A total thickness of this trilayer structure may be approximately the same as the thickness of the bilayer structure present in second portion 150 of substrate 100.

In an embodiment, after bilayer 300 or trilayer structure 335 is formed over first or second portions 140, 150 of substrate 100, an anneal is performed to interdiffuse the bilayer or trilayer structure. The anneal step may be performed at a range of suitable temperatures and times, e.g., 800-1100° C. for 1 second—1 hour. The anneal step causes the layers in the bilayer or trilayer to interdiffuse to form a single layer having a composition at least slightly different from the composition of the layers of the bilayer or trilayer structure. This may be desirable in order to eliminate sharp offsets in the band structure of the bilayer or trilayer structure that may affect device performance.

In an alternative embodiment, a crystalline epitaxial oxide layer disposed over semiconductor substrate selectively induces strain in first and second semiconductor layers disposed over the crystalline oxide layer.

Referring to FIG. 9, a crystalline epitaxial oxide layer 400 is disposed over semiconductor substrate 110. The crystalline oxide layer 400 includes a material having a lattice parameter selected to exert an appropriate strain, both in terms of level and direction, on first and second semiconductor layers 130, 200.

For example, crystalline oxide layer 400 may include or consist of a material such as strontium titanate (SrTiO₃ or other compositions) or lanthanum aluminum oxide (LaAlO₃ or other compositions), having a lattice parameter approximately equal to that of Si_(0.5)Ge_(0.5) that exerts a tensile strain on Si and a compressive strain on Ge. Therefore, a first semiconductor layer including or consisting of Si disposed on crystalline oxide layer 400 may be tensilely strained, and a second semiconductor layer including or consisting of Ge disposed on crystalline oxide layer 400 may be compressively strained.

The crystalline oxide layer 400 may include or consist of a multicomponent metal oxide such as a pervoskite-type oxide having the formula ABO₃ with B including at least one acid oxide containing a metal such as Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, or Cu, and A including at least one additional cation having a positive formal charge of from about 1 to about 3. Examples of such cations include cesium, strontium, barium, rubidium, yttrium, scandium, and lanthanum. Thus, examples of appropriate multicomponent metal oxides include but are not limited to: barium strontium titanate, barium strontium zirconate, barium strontium hafnate, lead titanate, yttrium aluminate, lanthanum aluminate, lead zirconium titanate, hafnium silicate, zirconium silicate, and rare earth-doped silicates.

Other examples of materials suitable for use as crystalline oxide layer 400 include metal silicate materials, such as strontium silicon oxide (SrSiO₄), zirconium silicon oxide (ZrSiO₄), and hafnium silicon oxide (HfSiO₄), hafnium oxide (HfO₂), zirconium oxide (ZrO₂), strontium titanate (SrTiO₃), lanthanum oxide (La₂O₃), yttrium oxide (Y₂O₃), titanium oxide (TiO₂), barium titanate (BaTiO₃), lanthanum aluminate (LaAlO₃), lanthanum scandium oxide (LaScO₃) and aluminum oxide (Al₂O₃).

Other options crystalline oxide layer 400 include any of several dielectric materials having lattice constants and structures similar to that of silicon. For example, cesium oxide (CeO₂), aluminum nitride (AlN) and lanthanum aluminum oxide (LaAlO₃) all have suitable lattice constants and crystalline structures.

Crystalline oxide layer 400 may be chosen to be deliberately lattice-mismatched to semiconductor substrate 110 to provide a lattice constant different therefrom for subsequent layer deposition. The crystalline oxide layer 400 material may be selected such that a major crystallographic plane of crystalline oxide layer 400 parallel to a surface of semiconductor substrate 110 differs from the crystallographic plane of that surface. This configuration may facilitate the desired lattice match or mismatch between crystalline oxide layer 400 and semiconductor substrate 110. For example, semiconductor substrate 110 may include silicon, SiGe, or germanium with a {100} surface, and crystalline oxide layer 400 may include an aforementioned material with a {200}, {110}, or {111} (i.e., not {100}) crystallographic plane parallel to the surface of semiconductor substrate 110. Such a combination may provide an effective in-plane lattice constant of crystalline oxide layer 400 suitable for lattice match or mismatch with semiconductor substrate 110 or subsequently deposited layers. This combination may also facilitate the formation of subsequently deposited layers, e.g., first and second semiconductor layers 130, 200, having a crystallographic orientation (i.e., surface crystallographic plane) different from a surface crystallographic orientation of semiconductor substrate 110 and/or having an in-plane rotation of the surface crystallographic plane different from that of semiconductor substrate 110. Such changes in crystalline orientation or rotation may result in enhanced carrier mobilities in devices subsequently fabricated on first and second semiconductor layers 130, 200.

Crystalline oxide layer 400 may have a single composition throughout its thickness. Alternatively, the composition of crystalline oxide layer 400 may vary throughout its thickness. For example, with a ternary oxide such as lanthanum aluminum oxide, the lanthanum content may gradually increase, thus increasing the lattice constant of the layer. Such grading of composition in crystalline oxide layer 400 may help prevent formation of defects due to lattice mismatch between crystalline oxide layer 400 and semiconductor substrate 110. Alternatively, crystalline oxide layer 400 may include multiple crystalline oxide layers, each having a different composition.

Crystalline oxide layer 400 may be formed by deposition, e.g., by CVD or ALD. The crystalline oxide layer 400 has a typical thickness t₆ of about 10-500 nm. Preferably, crystalline oxide 400 is thick enough to support subsequent deposition of first and second semiconductor layers 130, 200. Since many crystalline oxides have dielectric constants higher than that of silicon dioxide, a thick crystalline oxide 400 may be desirable to decrease capacitance.

In another embodiment, a thin amorphous layer (not shown) is formed on a top or a bottom surface of crystalline oxide 400 to prevent defect formation at an interface between crystalline oxide layer 400 and semiconductor substrate 110 or between the crystalline oxide layer and either of the first and second semiconductor layers 130, 200. The thin amorphous layer may include an oxide, e.g., SiO₂, SiGeO₂, and/or GeO₂. The thin amorphous layer may be formed by a thermal treatment after the formation of crystalline oxide 400, optionally in an ambient including oxygen.

Referring to FIG. 10, in another embodiment, a capping layer 410 may be formed on a top surface of crystalline oxide 400. The capping layer 410 may protect the crystalline oxide layer 400 from various wet chemical treatments of the substrate prior to the formation of first and second semiconductor layers. If capping layer 410 includes a material that can be removed selectively with respect to the underlying crystalline oxide 400, e.g., silicon nitride or a semiconductor, crystalline oxide 400 can be protected during subsequent masking and mask removal steps, e.g., those steps described below.

Referring to FIGS. 11-13, after the formation of crystalline oxide 400 and, optionally, capping layer 410, STI regions 160 may be defined with use of mask 180 as described above with reference to FIG. 2. Similarly, first semiconductor layer 130 may be defined over a region of the crystalline oxide layer disposed over the first portion 140 of the substrate and second semiconductor layer 200 may be defined over a region of crystalline oxide layer disposed over the second portion 150 of the substrate. First and second semiconductor layers 130, 200 may be chosen to be deliberately lattice-mismatched to the crystalline oxide layer 400 such that the semiconductor layers are under tensile or compressive strain. This strain may be biaxial in nature. In an embodiment, the lattice structure of crystalline oxide layer 400 is such that at least one of first and second semiconductor layers 130, 200 is primarily uniaxially strained in-plane.

Preferably, if optional capping layer 410 is initially disposed over the top surface of the crystalline oxide layer 400, then layer 410 is removed during the formation of first and second semiconductor layers 130, 200, e.g., by a wet or dry etch prior to deposition.

Subsequently, an nMOSFET may be formed, including a channel disposed in a portion of the first semiconductor layer 130 and a pMOSFET may be formed, including a channel disposed in a portion of the second semiconductor layer 200.

The embodiments described above include a continuous insulator layer disposed across a wafer. In some embodiments, the insulator layer may be discontinuous. Moreover, the insulator layer may include a first insulator layer including a first insulating material disposed over at least a first portion of the substrate and a second insulator layer including a second insulating material disposed over at least a second portion of the substrate. For example, different crystalline oxides may be formed selectively in NMOS and PMOS regions. An insulator layer such as SiO₂ may only be present below one or more device channel regions.

Referring to FIG. 14A, semiconductor substrate 110 may be used as a starting material. STI regions 160 extending into semiconductor substrate 110 may be defined as described above with reference to FIG. 2. After STI 160 is defined, the first portion 140 of the substrate 110 is exposed and the second portion 150 of the substrate is covered by mask 180, e.g., a mask defined after the completion of STI formation. Alternatively, mask 180 may include masking material used to protect those regions of the substrate 110 that are not exposed during STI formation; after STI formation, the masking material may be selectively removed from the first portion 140 of the substrate 110 where the nMOSFET will be formed, thereby exposing the first portion 140 of the substrate. Masking material used during STI formation may be, for example, silicon nitride CMP stop layer 182 disposed over pad oxide layer 184.

Referring to FIG. 14B, a first insulator layer 500 including a crystalline oxide material (and also referred to herein as “a first crystalline oxide layer”) may be defined over the first portion 140 of substrate 110. The first insulator layer 500 may be formed by deposition, e.g., by CVD or ALD, or a similar technique. Typically, the crystalline oxide layer is not formed selectively; rather, it is formed over the first portion 140 of the substrate 110 as well as over the mask 180 disposed over the second portion 150 of the substrate 110. Therefore, it may be preferable to mask off a region of the first insulator layer 500 disposed over the first portion 140 of the substrate 110, prior to removal of the remainder of the crystalline oxide material and mask disposed over the second portion 150 of the substrate 110. Alternatively, the first insulator layer 500 and a capping nitride layer (not shown) may be deposited over substantially the entire substrate 110. Then a CMP step may be performed to remove the portions of the capping nitride layer and first insulator layer 500 disposed over the second portion 150 of the substrate 110, stopping at a surface of the mask 180 disposed over the second region 150. Any residual nitride from the capping layer remaining over both the first and second portions 140, 150 of the substrate 110 may then be removed. This process also results in the formation of first insulator layer 500 over the first portion 140 of the substrate 110.

Referring to FIGS. 14B and 14C, after the formation of the first insulator layer 500, the mask 180 is removed, thereby exposing a top surface of the second portion 150 of the substrate. The mask 180 may be removed by, e.g., a wet etch. During the removal of the mask 180, a small portion of the STI 160 may also be removed, but not an amount sufficient to impact device performance. A second mask (not shown) is selectively formed over the first insulator layer 500, exposing the second portion 150 of the substrate. The second mask may include silicon nitride formed by, e.g., deposition, photolithography, and a wet or a dry etch. A second insulator layer 510, also referred to herein as “second crystalline oxide layer,” may formed over the second portion of the substrate 110 by a deposition technique such as CVD or ALD. After the formation of the second insulator layer 510, the second mask may be removed by, e.g., a wet etch. The first and second insulator layers 500, 510 may include the same materials and have the same thicknesses as the crystalline oxide layer 400 described above with reference to FIG. 9.

Referring to FIG. 15, a channel layer 520 may be formed over the first and second insulator layers 500, 510, as well as over STI region 160. A portion of the channel layer 520 disposed over the STI region 160 may be subsequently removed by, e.g., CMP. In an alternative embodiment, a first portion of the channel layer 520 is formed over the first insulator layer 500 after the formation of the first insulator layer and before the mask 180 is removed. Similarly, a second portion of the channel layer 520 is formed over the second insulator layer 510 after the formation of the second insulator layer and before the second mask is removed. The channel layer 520 may include a semiconductor material suitable for device channel formation, such as a group IV material, e.g., silicon, SiGe, germanium, or an array of carbon nanotubes; a III-V material such as gallium arsenide, indium arsenide, indium gallium arsenide, indium phosphide, gallium nitride, indium antimonide, gallium antimonide, gallium phosphide; or a II-VI material, and mixtures or alloys including one or more of the aforementioned materials.

In an embodiment, the channel layer 520 includes strained silicon. The first insulator layer 500 may include a material having a lattice constant larger than that of silicon, e.g., greater than 5.43 Å, resulting in the portion of the channel layer 520 disposed over the first insulator layer 500 to be tensilely strained, and thereby suitable for use as the channel material of an nMOSFET. The second insulator layer 510 may include a material having a lattice constant smaller than that of silicon, e.g., less than 5.43 Å, resulting in the portion of the channel layer 520 disposed over the second insulator layer 510 to be compressively strained, and thereby suitable for use as the channel material of a pMOSFET.

In an embodiment, a first portion of the channel layer 520 disposed over the first substrate portion 140 differs from a second portion of the channel layer 520 disposed over the second substrate portion 150. Different combinations of channel and crystalline oxide materials may result in improved device performance in different regions of the substrate.

In an embodiment, the use of different crystalline oxide materials in first and second substrate portion 140, 150 facilitates the deposition of channel layers thereover that have crystalline orientations or in-plane rotations different from each other, as discussed previously with reference to FIG. 15. The crystalline orientation and/or rotation for channel layer 520 may be different in first and second substrate portions 140, 150. Likewise, if different channel materials are used in each substrate portion 140, 150, the different channel materials may have different orientations and/or in-plane orientations. In an embodiment, the nMOSFET channel layer in first substrate portion 140 has a surface crystalline orientation defined by any of the {100} family of crystallographic planes, and the pMOSFET channel layer in second substrate portion 150 has a surface crystalline orientation defined by any of the {110} family of crystallographic planes. In another embodiment, the in-plane rotation of the nMOSFET channel material in substrate portion 140 is such that the nMOSFET channel is parallel to any of the <110> family of crystallographic directions, and the in-plane rotation of the pMOSFET channel material in substrate portion 150 is such that the pMOSFET channel is parallel to any of the <100> family of crystallographic directions.

This method of providing devices including channel materials of crystalline orientations and/or rotations different from each other may be superior to other methods in which regions of different orientations are provided prior to device fabrication. This method provides self-aligned channel materials of different crystalline orientations and/or rotations, i.e., only in desired regions bound by device isolation structures. Additionally, this method enables the fabrication of device channel layers of virtually any crystalline orientation or rotation, the choice of which is not bound by and does not necessarily relate to a crystalline orientation or rotation of an underlying substrate or of a handle wafer from which the layers may have been bonded. This method may also be used to provide channel layers of arbitrary crystalline orientation and/or rotation disposed over insulator layers.

Subsequently, an nMOSFET may be formed, including a channel disposed in a portion of the channel layer 520 disposed over the first insulator layer 500, and a pMOSFET may be formed, including a channel disposed in a portion of the channel layer 520 disposed over the second insulator layer 510.

The bilayer-on-insulator constructions described above and illustrated in, e.g., FIG. 6, may give favorable carrier transport behavior for FinFET-type devices, e.g., omega FETs, tri-gate FETs, etc. FinFETs typically have gates that wrap around a channel on at least two sides of a vertically oriented channel, allowing greater control of channel charge than in a single gate device. This configuration also has the potential to translate to higher drive current and lower stand-by leakage current. Devices related to the FinFET, such as the wrap-around gate FET (gate on both sides of as well as above the channel), allow even more channel charge control and hence even more potential for improved drive current and leakage current performance.

Referring to FIG. 16, in an embodiment, a FinFET may be defined as follows. A bilayer 600 is formed by deposition of two semiconductor layers over insulator layer 120, as described above with reference to FIGS. 1-3 and 6-8. The bilayer includes first semiconductor layer 610 disposed over the insulator layer 120 and second semiconductor layer 620 disposed over the first semiconductor layer 610. Both the first and second semiconductor layers 610, 620 may be biaxially strained. The first semiconductor layer 610 may be, e.g., biaxially tensilely strained, i.e., tensilely strained in a plane parallel to a top surface of the first semiconductor layer 610 and compressively strained in a plane perpendicular to the first semiconductor layer top surface. The second semiconductor layer 620 may be, e.g., biaxially compressively strained, i.e., compressively strained in a plane parallel to a top surface of the second semiconductor layer 620 and tensilely strained in a plane perpendicular to the second semiconductor layer top surface. In an alternative embodiment, either of the first semiconductor and second semiconductor layers 610, 620 is uniaxially strained.

Referring to FIGS. 17A and 17B as well as to FIG. 16, the first semiconductor layer 610 may be thicker than the second semiconductor layer 620 such that the sidewall of a fin 630 defined from the bilayer 600 is primarily formed from first semiconductor layer 610. For example, the first semiconductor layer 610 may have a thickness t₁ of 40-400 Å and the second semiconductor layer 620 may have a thickness t₂ of 10-100 Å. Thus, the bilayer 600 may have a total thickness t₅ of, e.g., 50-500 Å.

The bilayer 600 may be patterned to define a plurality of fins 630. In particular, fins 630 may be defined by the formation of a photolithographic mask (not shown) over the bilayer 600, followed by anisotropic RIE of the bilayer 600. Fins 630 may have a width w₁ of, e.g., 50-300 Å, and a height hi approximately equal to a thickness of the bilayer, e.g., 50-500 Å. The photomask/RIE steps also define source mesa region 632 and drain mesa region 634. Fins 630, source mesa region 632, and drain mesa region 634 include portions of the bilayer 600 not removed by RIE. The photolithographic mask is removed after the RIE of the bilayer 600.

Referring to FIG. 18, in another embodiment, fins may be formed by an alternative fabrication method. A single strained semiconductor layer is disposed over the insulator layer 120 and substrate 110. For example, the starting material may include a strained-semiconductor-on-insulator (SSOI) wafer, with first semiconductor layer 610 disposed over the insulator layer 120. The first semiconductor layer 610 may be bonded to the insulator layer 120. Alternatively, the insulator layer 120 may include a crystalline oxide, and the first semiconductor layer 610 may be deposited over the insulator layer. The first semiconductor layer 610 may be substantially unstrained, or tensilely or compressively strained.

Referring to FIG. 19, the first semiconductor layer 610 is patterned to define a plurality of fins 630. The fins 630 may be defined by the formation of a photolithographic mask (not shown) over the first semiconductor layer 610, followed by anisotropic RIE of the first semiconductor layer 610. The fins 630 may have a width w₁ of, e.g., 50-300 Å, and an initial height approximately equal to a thickness of the first semiconductor layer, e.g., 50-500 Å.

Referring to FIG. 20, a plurality of sidewall spacers 640 may be formed proximate sidewalls of the fins 630 as follows. A thin conformal insulator layer is deposited over the fins 630 and exposed portions of the insulator layer 120 between the fins. The conformal insulator layer may be, for example, silicon dioxide or silicon nitride, formed by, e.g., CVD, and may have a thickness of, e.g., 100-1000 Å. The sidewall spacers 640 is defined by the removal of portions of the conformal insulator layer by, e.g., an anisotropic dry etch, such that the remaining portions of the conformal insulator layer (which define spacers proximate the fin sidewalls) remain.

Referring also to FIG. 21, after the formation of the sidewall spacers 640, a top portion of the fins 630 includes exposed portions of a top surface of the first semiconductor layer 610 from which the fins 630 are formed. Second semiconductor layer 620 is selectively deposited on the exposed portions of the first semiconductor layer. The selective deposition may be performed by CVD, and the semiconductor precursor gas (or gases) may be accompanied by a Cl-containing species, e.g., C1 ₂ or HCl gas. Alternatively, the semiconductor precursor gas may be a chlorinated species, e.g., dichlorosilane (SiH₂Cl₂), trichlorosilane (SiHCl₃), silicon tetrachloride (SiCl₄), or germanium tetrachloride (GeCl₄). The second semiconductor layer 620 may have a thickness t₂ of, e.g., 10-200 Å. The spacers are removed, e.g., by a wet etch. In an embodiment, the top portion of the fins 630, i.e., the top portion of exposed first semiconductor layer 610, are removed by an in-situ etch prior to deposition of the second semiconductor layer 620. Such an etch may preserve the aspect ratio of subsequently formed bilayer fins 630.

Referring to FIGS. 21 and 16, the resulting fins 630 include second semiconductor layer 620 disposed over first semiconductor layer 610, like the fins formed from bilayer 600. In both embodiments, the top surface of the fin may include a material different from the material disposed along a major portion of the sidewalls of the fin. In both embodiments, both the sidewalls of the fins and the top surfaces may exhibit a same type of strain, i.e., compressive or tensile.

In summary, this bilayer fin formation may be accomplished by forming fins from an existing bilayer material. Alternatively, the bilayer fins may be initially defined by a single material that is then epitaxially capped with a second material. In both embodiments, the first semiconductor layer is preferably thicker than the second semiconductor layer.

Carrier transport in FinFET device constructions may occur along three different planes of the device: over a top surface of a fin and along first and second sides of the fin.

If a FinFET includes a single strained semiconductor layer disposed over an insulator layer, atoms biaxially strained along one plane will have an opposite type of strain in a perpendicular plane (e.g., Si that is tensilely strained in a horizontal direction will be compressively strained in the vertical direction due to Poisson deformation of the lattice). Hence, conduction along a sidewall of a fin covered by strained Si will be through a compressively strained layer, and conduction along a top of the fin will be through a tensilely strained layer.

In some embodiments, it may be preferable to have a construction exhibiting primarily the same strain on all three sides of the fin, i.e., both horizontally and vertically, in order to maximize the mobility of carriers conducting parallel to all three sides of the fin. Therefore, a tensilely strained film may be formed over the insulator layer and topped with a compressively strained film. Here, most of the sidewall conduction will be through the compressively strained sidewalls, and conduction along the topside of the fin will be through the other compressively strained material disposed over the tensilely strained film.

Referring to FIG. 22, in another embodiment, the fins are at least partially defined in crystalline oxide layer 400. The crystalline oxide layer may have a thickness t₇ of, e.g., 50-1000 Å. First semiconductor layer 610, having a thickness t₁ of, e.g., 10-200 Å, is disposed over the insulator layer including crystalline oxide. A photolithographic mask (not shown) may be defined over the first semiconductor layer 610. The photolithographic mask is, for example, photoresist. A hard mask 700, such as a silicon nitride hard mask, is defined over the first semiconductor layer 610. This hard mask 700 may enable subsequent formation of a semiconductor layer on fin sidewalls without also forming the semiconductor layer on the top surfaces of the fin. The hard mask may also act as a CMP stop (see below), and may have a thickness t₈ of, e.g., 100-1000 Å.

Referring to FIG. 23, fins 630 may be defined by anisotropic RIE of the first semiconductor layer 610 and the crystalline oxide layer 400. Fins 630 may have a width w₁ of, e.g., 50-300 Å, and a height hi approximately equal to a sum of the thickness t₁ of the first semiconductor layer and at least a portion of the thickness t₇ of the insulator layer 400, e.g., 50-500 Å.

Referring to FIG. 24, second semiconductor layer 620 may be conformally deposited over and between the fins. The second semiconductor layer 620 may be chosen to be deliberately lattice-mismatched to the crystalline oxide 400 such that the layer 620 is under tensile or compressive strain, as appropriate. The layer 620 may contain a semiconductor material identical to or substantially the same as that included in the first semiconductor layer 610.

Referring to FIG. 25, a thick oxide fill material 710, e.g., SiO₂, may be deposited over and between the fins 630.

Referring to FIGS. 25 and 26, a planarization step, such as a CMP step, may be performed to planarize the oxide fill material 710 and to remove a top portion of the second semiconductor layer 620 disposed over the hard mask 700, thereby exposing the hard mask disposed on the tops of the fins 630.

Referring to FIGS. 26 and 27, after planarization, the oxide fill material 710 may be removed by a wet or a dry oxide etch. Subsequently, an anisotropic dry etch may be used to remove portions of the second semiconductor layer 620 disposed over the hard mask 700 on the fins 630 and over the crystalline oxide layer 400 between the fins 630. The hard mask 700 can then be removed by a wet or dry etch, exposing the first semiconductor layer 610 disposed on the tops of the fins 630.

The resulting structure has a semiconductor material disposed on three sides of a crystalline oxide fin.

As discussed previously, crystalline oxide layer 400 may be deliberately lattice-mismatched to semiconductor substrate 110 for subsequent layer deposition. The crystalline oxide layer 400 material may be selected such that a major crystallographic planes of crystalline oxide layer 400 parallel and/or perpendicular to a surface of semiconductor substrate 110 is different from a crystallographic plane of the surface of semiconductor substrate 110. This configuration may facilitate the desired lattice match or mismatch between crystalline oxide layer 400 and semiconductor substrate 110.

For example, semiconductor substrate 110 may include or consist of silicon, SiGe, or germanium with a {100} surface, and crystalline oxide layer 400 may include an aforementioned material with a crystallographic plane other than {100}, e.g., {200}, {110}, or {111}, parallel to the surface of semiconductor substrate 110. Such a combination may provide an effective lattice constant of crystalline oxide layer 400 suitable for lattice match or mismatch with semiconductor substrate 110 or subsequently deposited layers. This combination may also facilitate the formation of subsequently deposited layers, e.g., first and second semiconductor layers 610, 620, having a crystallographic orientation (i.e., surface crystallographic plane) different from that of semiconductor substrate 110. Such changes in crystalline orientation may result in enhanced carrier mobilities in devices subsequently fabricated over fins 630.

This degree of freedom in selecting crystallographic orientation may enable the formation of FinFETs having channel layers of arbitrary crystalline orientation, e.g., having some FinFET channels of different crystalline orientation with respect to others, without necessitating complicated layout issues, device rotations, or wafer bonding schemes. For example, in an embodiment, a first FinFET including a crystalline oxide and a channel layer having a substantially {100} crystalline orientation may be fabricated adjacent to a second FinFET including a crystalline oxide and a channel layer having a substantially {110} crystalline orientation. Furthermore, the first and second FinFETs may be fabricated such the devices (e.g., the fins) are oriented in parallel to each other. Forming such a configuration may be facilitated by the use of different crystalline oxides for each of the first and second FinFETs. In this embodiment, the first FinFET may be an n-channel device and the second FinFET may be a p-channel device.

After the formation of the fins by any of the methods described above, the completion of the FinFET fabrication may continue as follows.

Referring to FIG. 28 as well as to FIGS. 17A and 17B, a gate insulator layer 715 is formed over the fins 630 and exposed underlying insulator layer 120 or crystalline oxide layer. Gate insulator layer 715 is conformally formed over fins 630, as well as over source and drain mesa regions 632, 634. Gate insulator layer 715 may include, e.g., SiO₂, SiO_(x)N_(y), silicon nitride (Si₃N₄ or other compositions), barium oxide (BaO), strontium oxide (SrO), calcium oxide (CaO), tantalum oxide (Ta₂O₅), titanium oxide (TiO₂), zirconium oxide (ZrO₂), hafnium oxide (HfO₂), aluminum oxide (A1 ₂O₃), lanthanum oxide (La₂O₃), yttrium oxide (Y₂O₃), yttrium aluminate, lathanum aluminate, lanthanum silicate, yttrium silicate, hafnium silicate, zirconium silicate, and doped or undoped alloys, mixtures or multilayers, thereof and have a thickness t₉ of, e.g., 10-100 Å. In some embodiments, gate insulator layer 715 is grown, and is therefore formed only over exposed semiconductor surfaces, i.e., over top surfaces of fins 630 and source and drain mesa regions 632, 634. In other embodiments, gate insulator layer 715 is deposited, and is therefore formed over an entire top surface of the fins and exposed portions of the underlying insulator layer 120 or crystalline oxide.

Referring to FIGS. 29A and 29B, a gate electrode material 720 is conformally formed over gate insulator layer 715, including over fins 630. Gate electrode material 720 may include a suitably conductive material such as, for example, doped polysilicon, doped polycrystalline SiGe, Al, Ag, Bi, Cd, Fe, Ga, Hf, In, Mn, Nb, Y, Zr, Ni, Pt, Be, Ir, Te, Re, Rh, W, Mo, Co, Fe, Pd, Au, Ti, Cr, Cu, and doped or undoped alloys, mixtures or multilayers thereof, deposited by ALD or CVD, such as by UHVCVD, APCVD, LPCVD, or PECVD, and have a thickness t₁₀ selected from the range of, e.g., 100-2000 Å. A photolithographic mask (not shown) is formed over gate electrode material 720. Portions of gate electrode material 720 are selectively removed by, e.g., RIE to define a gate 730 crossing over fins 630, and terminating in a gate contact area 740. Portions of gate insulator layer 715 are exposed (or even removed) by the RIE of gate electrode material 720.

Referring to FIGS. 30A and 30B, a plurality of dopants are introduced into source and drain mesa regions 632, 634 to define a source 750 and a drain 760. To form an n-type FinFET, dopants such as arsenic, antimony, or phosphorus may be implanted into mesa regions 632,634. Suitable implantation parameters may be, for example, arsenic with a dose of 2×10¹⁵ atoms/cm² implanted at an energy of 10-50 kilo-electron volts (keV). To form a p-type FinFET, dopants such as boron or indium may be implanted into mesa regions 632, 634. Suitable implantation parameters are, for example, boron, with a dose of 2×10¹⁵ atoms/cm² at an energy of 3-15 keV. For the formation of a CMOS device, NMOS regions may be protected by a mask during the implantation of p-type dopants into PMOS regions. Similarly, PMOS regions may be protected by a mask during the implantation of n-type dopants into NMOS regions. A suitable mask for both types of implantation may be, e.g., photoresist.

During the introduction of dopants into source and drain mesa regions 632, 634, a plurality of gate dopants 775 may also be introduced into gate 730 and gate contact area 740. Gate dopants 770 serve to increase a conductivity of gate electrode material 720. Gate dopants 770 may be, for example, implanted arsenic, antimony, or phosphorous ions for an n-type FinFET.

Dopants for both n-type and p-type FinFETs may be implanted at an angle of 20-50°, with zero degrees being normal to the substrate 110. Implanting at an angle may be desired in order to implant ions into a side of exposed fins 630 and also into a side of the vertical surfaces of gate electrode material 720.

Referring to FIGS. 31A and 31B, a blanket layer of spacer insulator material is formed over the substrate 110, including over gate 730, gate contact area 740, source 750, and drain 760. Spacer insulator material may be, for example, SiO₂ or Si₃N₄ deposited by CVD and have a thickness of, for example, 100-1000 Å. Subsequently, portions of spacer insulator material are removed by an anisotropic RIE to define a plurality of sidewall spacers 775 proximate vertical surfaces, such as fins 630, gate 730, and gate contact area 740. Horizontal surfaces, such as top surfaces of fins 630, are substantially free of the spacer insulator material.

After the RIE definition of sidewall spacers 775, the portions of gate insulator layer 715 exposed by the RIE of gate electrode material 720 may be removed from top surfaces of source 750, and drain 760 by, e.g., a dip in hydrofluoric acid (HF), such as for 5-30 seconds in a solution containing, e.g., 0.5-5% HF. Alternately, this removal may be via RIE, with an etchant species such as, e.g., CHF₃.

Referring to FIGS. 32A and 32B, a salicide is selectively formed over the substrate 110 to provide low-resistance contacts to the source and drain regions and the gate electrode as follows. A conductive layer is formed over the substrate 110. For example, a metal such as titanium, platinum, zirconium, cobalt, nickel, or alloys, mixtures, or multilayers thereof is deposited by, e.g., CVD or sputtering, with the conductive layer having a thickness of, e.g., 50-200 Å. An anneal is performed to react the conductive layer with the underlying semiconductor, e.g., exposed portions of gate 730 and gate contact area 740, to form salicide 780 including, e.g., cobalt silicide or nickel silicide. Anneal parameters may be, for example, 400-800° C. for 1-120 seconds. Unreacted portions of the conductive layer disposed directly over insulator material, such as exposed portions of insulator layer 120 and sidewall spacers 775, are removed by a chemical strip. A suitable chemical strip may be a solution including H₂SO₄:H₂O₂ at a ratio of 3:1. A second anneal may be performed to further lower resistivity of salicide 780. The second anneal parameters may be, for example, 600-900° C. for 1-120 seconds. A FinFET 790 includes fins 630, gate insulator 715, source 750, drain 760, and gate 730, and an exemplary FinFET 790 having three fins 630 is illustrated in FIG. 32B. The three fins 630 share a common source 750 and a common drain 760. A single transistor may have multiple fins to increase current drive in comparison to a transistor with a single fin. The semiconductor material disposed in each fin 630 defines a device channel.

In an alternative embodiment, gate dielectric material may be removed from the top surfaces of the source and drain mesa regions immediately after the RIE of the gate electrode. In some embodiments, raised source and drain regions may be formed, as described above with reference to FIGS. 4 and 5.

Referring to FIG. 14C as well as to FIGS. 33A-33C, a structure including first and second insulator layers 500, 510 disposed over first and second portions 140, 150 of semiconductor substrate 110, respectively, may be used to fabricate a first FinFET 790 a and a second FinFET 790 b that are physically parallel to each other and have channels with different crystalline orientation. Such first and second FinFETs may be fabricated as follows.

First insulator layer 500 disposed over the first portion 140 of semiconductor substrate 110 may include a first crystalline oxide, and second insulator layer 510 disposed over the second portion 150 of semiconductor substrate 110 may include a second crystalline oxide. The first and second crystallographic oxides may be identical, substantially the same, or substantially different. First semiconductor layer 610 a comprising a first semiconductor material is disposed over the first insulator layers 500, and first semiconductor layer 610 b comprising a second semiconductor material is disposed over the second insulator layer 510. In an embodiment, first and second semiconductor materials are identical or substantially the same. In an alternative embodiment, first and second semiconductor materials are different. In both embodiments, the first semiconductor material disposed in first semiconductor layer 610 a has a first crystalline orientation, the second semiconductor material disposed in first semiconductor layer 610 b has a second crystalline orientation, and the first and second crystalline orientations are different.

A first plurality of fins 630 a disposed over the first insulator layer 500, and a second plurality of fins 630 b disposed over the second insulator layer 510 are defined as discussed above with reference to FIG. 23-27, with a second semiconductor layer 620 a comprising the first semiconductor material disposed on the vertically oriented sidewalls of the fins 630 a, and a second semiconductor layer 620 b comprising the second semiconductor material disposed on the vertically oriented sidewalls of fins 630 b. At least one fin from the first plurality of fins 630 a may be parallel to at least one fin from the second plurality of fins 630 b. The term “vertically oriented” does not denote a particular absolute orientation; rather, it is used herein to mean an orientation that is substantially perpendicular to a top surface of the substrate over which the fin is formed.

In the embodiment in which the first and second semiconductor materials are different, second portion 150 of substrate 110 may be the portion of the substrate including second insulator layer 510, and may be protected by a masking material during fabrication of the first FinFET 790 a. Likewise, after the first FinFET 790 a is fabricated, it may be protected by a masking material during fabrication of the second FinFET 790 b. Alternatively, the same channel material, i.e., semiconductor material, may be deposited over both first and second insulator layers 500, 510 as described above with respect to FIG. 15, and the first and second FinFETs 790 a, 790 b may be fabricated in turn as described above with reference to FIGS. 22-27.

The first FinFET 790 a includes fins 630 a, gate insulator 715, source 750, drain 760, and gate 730. The second FinFET 790 b includes fins 630 b, gate insulator 715, source 750, drain 760, and gate 730. Both FinFETs 790 a, 790 b may include gate contact areas 740, sidewall spacers 775, and salicide regions 780.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting on the invention described herein. 

1. A structure comprising: a substrate having an insulator layer disposed thereon; and a fin field-effect transistor disposed over the substrate, the fin field-effect transistor including: a source region and a drain region disposed in contact with the insulator layer; at least one fin extending between the source and the drain regions and comprising a bilayer; a gate disposed above the bilayer, extending over at least one fin and between the source and the drain regions; and a gate dielectric layer disposed between the gate and the fin, wherein the bilayer comprises a second semiconductor material disposed over a first semiconductor material, and the first semiconductor material is different from the second semiconductor material. 2.-3. (canceled)
 4. The structure of claim 1, wherein the first semiconductor material includes at least one member of the group consisting of silicon, SiGe, germanium, an array of carbon nanotubes, and mixtures or alloys thereof.
 5. The structure of claim 1, wherein the first semiconductor material includes at least one member of the group consisting of gallium arsenide, indium arsenide, indium gallium arsenide, indium phosphide, gallium nitride, indium antimonide, gallium antimonide, gallium phosphide, and mixtures or alloys thereof.
 6. (canceled)
 7. The structure of claim 1, wherein the second semiconductor material includes at least one member of the group consisting of silicon, SiGe, germanium, an array of carbon nanotubes, and mixtures or alloys thereof.
 8. The structure of claim 1, wherein the second semiconductor material includes at least one member of the group consisting of gallium arsenide, indium arsenide, indium gallium arsenide, indium phosphide, gallium nitride, indium antimonide, gallium antimonide, gallium phosphide, and mixtures or alloys thereof. 9.-10. (canceled)
 11. The structure of claim 1, wherein the first semiconductor material is tensilely strained and the second semiconductor material is compressively strained.
 12. The structure of claim 1, wherein the first semiconductor material is compressively strained and the second semiconductor material is tensilely strained.
 13. The structure of claim 1, wherein the gate dielectric is disposed proximate the first semiconductor material and the second semiconductor material.
 14. (canceled)
 15. A structure comprising: a substrate; a first insulator layer disposed over at least a first portion of the substrate; a second insulator layer disposed over at least a second portion of the substrate; a first fin field-effect transistor disposed over the substrate, the first fin field-effect-transistor including: a first source region and a first drain region disposed over and in contact with the first insulator layer; a first fin extending between the first source and the first drain regions, the first fin comprising a first semiconductor material disposed on at least one vertically oriented sidewall of the first fin; a first gate, disposed above the substrate, extending over the first fin and between the first source and the first drain regions; a first gate dielectric layer disposed between the first gate and the first fin; and a second fin field-effect transistor disposed over the substrate, the second fin field-effect-transistor including: a second source region and a second drain region disposed over and in contact with the second insulator layer; a second fin extending between the second source and the second drain regions and comprising a second semiconductor material disposed on at least one vertically oriented sidewall of the second fin; a second gate, disposed above the substrate, extending over the second fin and between the second source and the second drain regions; and a second gate dielectric layer disposed between the second gate and the second fin, wherein the first semiconductor material has a first crystalline orientation, the second semiconductor material has a second crystalline orientation, and the first and second crystalline orientations are different. 16.-17. (canceled)
 18. The structure of claim 15, wherein the first fin and second fin are substantially parallel.
 19. The structure of claim 15, wherein the first semiconductor material and the second semiconductor material are substantially the same.
 20. The structure of claim 15, wherein the first crystalline orientation is selected from a {100} family of crystalline planes.
 21. The structure of claim 15, wherein the first crystalline orientation is selected from a {110} family of crystalline planes.
 22. The structure of claim 15, wherein the first fin field-effect transistor comprises an n-channel device and the second fin field-effect transistor comprises a p-channel device.
 23. A structure comprising: a substrate; a first fin field-effect transistor disposed over the substrate; and a second fin field-effect transistor disposed over the substrate; wherein the first fin field-effect transistor comprises a first semiconductor material has a first crystalline orientation, the second fin field-effect transistor comprises a second semiconductor material has a second crystalline orientation, and the first and second crystalline orientations are different.
 24. A method for forming a structure, the method comprising: providing a substrate having an insulator layer disposed thereon, and a bilayer disposed in contact with the insulator layer, the bilayer including a second semiconductor layer disposed over a first semiconductor layer; and thereafter forming a fin field-effect transistor on the substrate by: patterning the bilayer to define a source region, a drain region, and at least one fin disposed between the source and the drain regions, forming a gate dielectric layer at least a portion of which is disposed over the fin, and forming a gate over the gate dielectric layer portion disposed over the fin, wherein a thickness of the first semiconductor layer is greater than a thickness of the second semiconductor layer such that a sidewall of the fin is primarily defined by the first semiconductor layer.
 25. The method of claim 24, wherein the bilayer comprises at least one of a group II, a group III, a group IV, a group V, or a group VI element.
 26. The method of claim 24, wherein the bilayer comprises a strained semiconductor layer.
 27. The method of claim 26, wherein the strained semiconductor layer is tensilely strained.
 28. The method of claim 26, wherein the strained semiconductor layer is compressively strained. 29.-31. (canceled)
 32. The method of claim 24, wherein the insulator layer has a thickness between approximately 10 and approximately 50 nm.
 33. The method of claim 24, wherein the sum of the thickness of the first semiconductor layer and the thickness of the second semiconductor layer is approximately 0.25 to approximately 0.7 times a gate length of the fin field-effect transistor.
 34. The method of claim 24, wherein the sum of the thickness of the first semiconductor layer and the thickness of the second semiconductor layer is less than approximately 50 nm.
 35. The method of claim 24, wherein the thickness of the first semiconductor layer is between approximately 5 and approximately 10 times greater than the thickness of the second semiconductor layer.
 36. The method of claim 24, wherein the thickness of the second semiconductor layer is between approximately 1 and approximately 10 nm. 